A CUTTER FOR A BORING HEAD, A DEVICE FOR ACCOMMODATING THERMALLY EXPANDING GREASE, AND A METHOD OF GREASING BEARINGS IN A CUTTER

Abstract: The present invention relates to cutter (10) for a raise boring head, a device for accommodating thermally expanding grease and a method for greasing bearings in a cutter, said cutter (10) being rotatably mounted, via a shaft (12) of the cutter (10), in a saddle secured to the raise boring head, bearings (18, 20) provided between the shaft (12) and a roller body (16) of the cutter (10) in order to make it possible for the roller body (16) to rotate relative to the shaft (12), seals (33) between the shaft (12) and the roller body (16), and boring/hole means (38, 48, 50) for introducing lubrication means into the interior of the cutter (10). The invention is characterized by a retainer plug (52) having an intermediate portion (56) with reduced diameter in order to provide an expansion space for the grease in the cutter (10).

Description: A cutter for a boring head, a device for accommodating thermally expanding grease, and a method of greasing bearings in a cutter . The present invention relates to a cutter for a boring head, preferably a raise boring head, (e.g. see U.S. RE. 34,167 disclosing a raise boring head), and in particular to a lubrication mechanism of such a cutter. A shaft of the cutter is rotatably mounted in a saddle secured to the raise boring head. Bearings provided between the shaft and an outer roller body of the cutter make it possible for the roller body to rotate relative to the shaft and for cutting elements on the roller body to perform a cutting operation. Seals disposed between the shaft and the roller body seal-in lubrication introduced into the bearings. ^ When cutters of the type mentioned above are working it is necessary that the bearings are embedded in a lubricant, preferably grease, i.e. the space between the shaft and the cutter is filled with grease. This is done in order to rmnimize the friction when the roller body is rotated relative to the shaft. By having a low internal friction in the bearings, the life of the cutter is kept at an acceptable level. However, it has turned out that under very tough working conditions, i.e., when the cutter is subjected to a heavy load, much heat is generated by rotation of the roller body relative to the shaft and by friction as the cutter works the rock. Due to the heat generation the grease expands and the internal pressure of the cutter rises. Under such conditions it occasionally happens that the internal pressure of the cutter reaches a level where the sealing means are not able to withstand said internal pressure, i.e., the seals collapse and the grease emerges from the bearings. It is readily understood that if the seals collapse then the cutter will rapidly breakdown. From DE-PS 27 42 019 a cutter for a tunnel boring machine is previously known, the cutter being equipped with pressure relief valves connected to certain ends of the internal grease passages. Other ends of the internal grease CONFIRMATION passages are equipped with nipples for introducing grease into the internal grease passages. The function of the pressure relief valves is to allow passage of excessive grease both when grease is primarily introduced into the interior of the cutter as well as when regreasing of the cutter is effected. However, if the cutter according to DE-PS 27 42 019 is subjected to heavy loads and consequently a thermal expansion of the grease takes place, the pressure will increase until the pressure relief valves open. Thus, it is absolutely necessary that the valves function properly to avoid damages primarily to the seals and subsequently to the bearings. It is well known that the working conditions of cutters are extremely tough and that a considerable amount of dirt/cuttings adhere to the cutter. Therefore, there is considerable risk that the pressure relief valves become clogged and consequently not opening at their nominal pressure. The aim of the present invention is to present a cutter that can be used under extreme tough working conditions, especially when heat is generated inside the cutter and the grease expands. The aim of the present invention is realized by a cutter that has been given the characteristics of the appending claims. The present invention also relates to a grease retainer plug per se. An additional aspect of the invention involves a method of greasing bearings which are disposed in a cutter. Below, an embodiment of the cutter according to the present invention is described, reference being made to the accompanying drawings, wherein: Fig. 1 shows a plan view of a prior art raise boring head; Fig. 2 shows a longitudinal section through a cutter when grease is introduced into the interior of the cutter; Fig. 3 shows a longitudinal section through the cutter according to Fig. 1 when the cutter is in working condition; and Fig. 4 shows a longitudinal section through a retainer used in Fig. 2. Depicted in Fig. 1 is a conventional raise boring head 1 comprising a rotary carrier 2 on which is mounted a plurality of cutters 10'. Each cutter is mounted in a saddle comprised of two arms 3 disposed on opposite sides of the cutter. In accordance with the present invention the cutters 10' are in the form of cutters 10 depicted in Figs. 2-4. Each cutter 10 includes a shaft 12 having a longitudinal center axis 14. The shaft 12 is mounted in the saddle, the saddle being secured to the body 2 of the boring head. (See US Patent No. RE 34,167 for a description of a conventional saddle and boring head, the disclosure of that patent having incorporated by reference herein.) A roller body 16 is rotatably mounted on the shaft 12 via two sets of bearings 18 and 20, respectively. The roller body carries cutting elements 16'. The bearings 18 are received in a first circumferential channel or groove 22 formed in an outer periphery of the shaft 12, while the bearings 20 are received in a second circumferential channel or groove 24 formed in an inner periphery of the roller body or hub 16. The roller body 16 is locked axially relative to the shaft 12 by locking means 26, preferably including an annular row of balls 26 disposed in cooperating third and fourth circumferential channels or grooves 28 and 30, formed respectively in the shaft 12 and the roller body 16. Between the axial ends of the roller body 16 and the shaft 12 the cutter 10 is provided with seal retainer means 32 supporting seals 33 that prevents grease from leaking out from the interior of the cutter 10. Both seal retainer means 32 are equipped with first relief holes 34 in which conical plugs 36 are mounted to prevent grease from leaking out through the holes 34. The function of the first relief holes 34 is explained more in detail below. The cutter 10 is provided with an axial boring 38 that extends along axis 14 from one end of the shaft 12, i.e., in the disclosed embodiment from the end of the shaft 12 where the roller body 16 has its smallest outer diameter. The axial boring 38 extends about halfway of the length of the shaft 12. Close to the inner end of the boring 38, a generally radial boring 40 extends from the axial boring 38 to the third groove 28. The boring 40 is used to install the balls 26' of the locking means 26. When the balls have been installed a ball plug 42 and a spacer plug 44 are mounted in the boring 40. To insert grease into the cutter, a filling plug 46 is removably mounted in the axial boring 38 by a frictional slide fit. For access reasons the filling plug 46 extends out of the boring 38 and is provided with a grease nipple 47 and an internal axial feeding hole 49 that extends from the nipple 47 to the opposite end portion of the filling plug 46. A radially extending discharge hole 51 emanates from the feeding hole 49 and perforates the envelope surface of the filling plug 46. The ball plug 42 is provided with two axially extending holes 48, 48' which are parallel to and offset from the longitudinal center axis of the ball plug 42, while the spacer plug 44 is provided with one axially extending central hole 50. The reason why the holes 48, 48' of the ball plug 42 are offset from the axis of plug 42 is to prevent the area of contact between the balls of the locking means 26 and the ball plug from blocking the entry of grease into the locking means 26. The channel 28 communicates with both of the channels 12 and 24, so that grease introduced into the channel 28 also travels to the bearings 18 and 20. In Fig. 2 the cutter 10 is shown in condition for being greased or regreased. A grease gun (not shown) is attached to the grease nipple 47 and grease is pumped into the cutter by the grease gun. The first relief holes 34 are used to control the level of the grease inside the cutter 10. That is, excess grease is forced through the holes 34. The conical plugs 36 are mounted in the first relief holes 34 when the greasing or regreasing is completed. The filling plug 46 is then removed, leaving the bore 38 essentially grease-free, and is replaced by a retainer plug 52 (see Figs. 3 and 4) that has a shorter length compared to the filling plug 46. The retainer plug is also mounted via slide fit. However, the retainer plug 52 is secured against axial displacement outwardly by a snap ring 54 which fits in a recess 54' formed in the boring 38 (see Fig. 2). The retainer plug 52 has an intermediate portion 56 with reduced diameter and consequently a circumferential expansion space 57 is provided between the reduced diameter portion 56 and the wall of the boring 38. At its front end the retainer plug 52 bears against the bottom of the radial boring 38. At its rear end the retainer plug 52 is provided with second relief holes 58 that communicate with a center passage 70 of a conventional pressure relief valve 60 of any suitable type which is threadedly connected in a rear end of the retainer plug. A cap 62 covers the free end of the pressure relief valve 60 in order to prevent the valve 60 from being clogged by cuttings/dirt. The cap is r mounted with a frictional slide fit or snap fit in the boring 38. The cutter 10 according to the invention functions in the following way. When a cutter 10 is set under working conditions it rotates and is subjected to heavy loads. This means that due to friction heat is generated in the bearings 18,20 and the locking means 26 of the cutter 10 and consequently also the grease is heated. When the grease is heated it expands and since the seal retainers 32 prevent grease from leaking out between the roller body 16 and the shaft 12, the grease enters into the expansion space 57. If the grease expands to such an extent that the space 57 becomes completely filled with grease then there is a possibility for the grease to emit through the openings 58 and the pressure relief valve 60. However, under normal conditions the expansion space 57 should be sufficient to accommodate the expansion of the grease. In case grease emits through the pressure relief valve 60 the cap 62 will be displaced outwardly towards the opening of the boring 38, thereby expanding the volume formed between the valve 60 and the cap 62. When the cap 60 reaches the opening, further displacement is prevented due to the presence of a conventional bolt 72 securing the shaft 12 in the saddle. (See the broken line position of the cap 62 shown in Fig. 3). This arrangement will permit thermal expansion of the grease while effectively prevent cuttings/dirt from clogging the pressure relief valve 60. It will be appreciated that any other suitable means could be provided for limiting the outward sliding movement of the cap 62. The embodiment described above relates to a cutter for a raise boring head although it is also possible to practice the invention in connection with cutters/discs for tunnel boring heads. It is also possible within the scope of the present invention to use bearings including tapered roller bearings. In such a case there is normally no need for axial locking means since the tapered roller bearings give support both in radial and in axial directions. Thus, the retainer plug 52 would retain only grease since the spacer plug 44 could be omitted. Although present invention has been described in connection with a preferred embodiment thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims: Claims 1. Cutter (10) for a boring head, comprising: a non-rotatable shaft (12) defining a longitudinal axis (14), a roller body (16) mounted on said shaft for rotation relative thereto about said axis, said roller body carrying cutting elements (16'), bearings (18,20) disposed in a channel (22,24) disposed between said shaft and roller body, said channels containing a lubricant adapted to expand thermally during a cutting operation, seals (33) arranged between said shaft and roller body for resisting the escape of said lubricant, a passage (38) formed in said shaft and communicating with said channel for accommodating the introduction of lubricant thereto, characterized in that a device for accommodating thermally expanding lubricant from said channel while preventing the escape of such thermally expanding lubricant from said passage, said device comprising a plug (52) disposed in said passage, said plug having opposite ends and a space disposed between said ends, said space communicating with said channel for receiving thermally expanding lubricant therefrom. 2. Cutter according to claim 1, characterized in that the plug (52) is provided with an intermediate portion (56) having a reduced diameter compared to the rest of the plug (52), said intermediate portion (56) being surrounded by a space (57) that circumferentially is surrounded by the boring (38), said space (57) communicating with the bearings (18,20). 3. Cutter according to claim 2, characterized in that the space (57) communicates with the bearings (18,20) via spacer means (42,44) that are located between the plug (52) and axial locking means (26) for the roller body (16). 4. Cutter according to claims 2 or 3, characterized in that the plug (52) at one end is provided with a pressure relief valve (60) that via holes (58) is communicating with the space (57). 5. Cutter according to claim 4, characterized in that a cap (62) covers the free end of the pressure relief valve (60). 6. Cutter according to any of the preceding claims, characterized in that the plug (52) is mounted in the boring (38) by frictional slide fit. 7. A cutter for a boring head, comprising: a non-rotatable shaft (12) defining a longitudinal axis (14), a roller body (16) mounted on said shaft for rotation relative thereto about said axis, said roller body carrying cutting elements (16'), bearings (18,20) disposed in a channel (22,24) disposed between said shaft and roller body, said channels containing a lubricant adapted to expand thermally during a cutting operation, seals (33) arranged between said shaft and roller body for resisting the escape of said lubricant, a passage (38) formed in said shaft and communicating with said channel for accommodating the introduction of lubricant thereto, characterized in that a device for accommodating thermally expanding lubricant from said channel while preventing the escape of such thermally expanding lubricant from said passage, said device comprising first and second members disposed in said passage, said first member disposed closer to said channel, and said second member disposed closer to an open end of said passage, said first and second members being relatively movable in said passage in response to the entry therebetween of thermally expanding lubricant from said channel for increasing the size of a space formed between said first and second members to accomodate said thermally expanding lubricant, said second member blocking the escape of lubricant from said open end of said passage. 8. A device insertable into a passage of a cutter (10) for a raise boring head, characterized in that the device comprises a plug (52) having an intermediate portion (56) of reduced diameter for forming a lubricant-receiving space. 9. A device according to claim 8, characterized in that the plug (52) at one end is provided with a pressure relief valve (60) and in that a cap (62) covers the free end of the pressure relief valve (60). 10. A method of greasing bearings disposed in a cutter (10), said cutter comprising a stationary shaft (12) and a roller body (16) mounted on said shaft for rotation relative thereto about an axis (14) characterized in that the method comprises the steps of: -inserting a filling plug (46) into an axial bore (38) of said shaft; -forcing grease through an axial feeding hole (49) of said filling plug so that grease exits an outlet of said feeding hole and enters a bearing channel disposed between said shaft and roller body and in which bearings (18,20) are disposed; -removing said filling plug (46) from said bore, leaving said bore generally grease-free; and -installing a grease retainer plug (52) into said bore and locking said retainer plug in place in said bore.

Inventors: STRAND GOERAN, STRAND, GOERAN
Applicants: SANDVIK AB
Application year: 1994
Main classification: E21B10
IPC codes: E21B10